Swiss drugmaker Roche has said it plans to offer shareholders $5.7 billion (SFr5.29 billion) for San Diego-based DNA diagnostics company Illumina.

Roche reckons the deal will accelerate routine clinical use of DNA testing. The Basel-based holding added that buying Illumina would strengthen Roche's position in diagnostics because the companies' technologies are complementary.

Roche's planned tender offer of $44.50 per share would represent an 18 per cent premium over Tuesday's closing price of $37.69 for Illumina shares.

Roche said the offer price is 64 per cent higher than the last closing price before speculation surfaced in December that Roche was considering acquiring the American firm.

Roche, which has more than 80,000 employees and specialises in cancer diagnosis and diabetes management, said it has tried to negotiate a deal, but Illumina has declined to participate.

If the buyout proceeds, Roche plans to move the headquarters for its applied science business to San Diego but maintain operations for the unit in Penzberg, Germany, where it's now based.

Illumina has told shareholders it would look at the offer before making any recommendations on whether to sell.

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